T

Tom Martin

Well Known Member
This morning I was digging a trench from my field of flooded corn in an attempt to get a large pond of water away from new seedings. Armed with rubber boots and a shovel I was having fun watching the water move down my new trench. It was interesting to watch the interaction with grass and debris as the water flowed. There was a lot of previous floating crop residue and it was easy to see the flow of water by observing these bits of old corn plants.
I stuck my shovel handle in the stream of debris and it was neat to see how the turbulence showed up downstream of the shovel. I went to the shop and retrieved an unused gear faring and shoved it in the stream. The particles flowed nicely around the shape and the two flows reattached smoothly aft of the gear faring. Debris tended to pile up in front of the shovel handle but not the gear faring. The maximum thickness of the faring was very close to the size of the handle. In the flow aft of the shovel handle you can see particles that are actually being pulled back to the handle and then swirl in the turbulent area.
The debris that piled up in front of both items did greatly disrupt the flow and reminded me of videos I had seen of ice on aircraft wings.
I took a short video
http://www.youtube.com/watch?v=G9MIvzDcwjg
 
Hi Tom
Interesting visualisation : but I think the Reynolds No would be v.low by comparison with RV-in-air !!

BTW, I have many happy hours in your RV4 'Raven' over the UK : now have ZK-RVN in NZ - I guess your RV4 hooked me !!
 
Aerodynamics for dummies

Finally, an aerodynamics lesson I can understand! Next time it rains take your wing to the ditch, stick it in the mud, and shoot some more video :D
 
Very cool demonstration. Keep up the good work!!

BTW, this kind of thinking is why Tom has a blazing fast Rocket.
 
It's a great visual demonstration and how it can be that a small round wire can have the same drag as an entire airfoil.
 
Last week, the International hang-gliding competition was held in central Georgia and Jenny and I went on Tuesday with huge thermals everywhere for their 63 mile triangular cross-country trip.

I was amazed at all the latest technology involved in something as simple as a hang-glider. The leading edges, up to the thickest point, have zillions of little squares, about 1/8th" square and .0010 thick, so I asked our guide about it. He said, "Just like the dimples on a golf ball, they provide extra lift." I told him that we always had super slick wings on our gliders and he replied that at 30-40 MPH, this works better.

These little suckers have reached 20:1 glide ratios already.

Best,
 
pierre smith said:
Last week, the International hang-gliding competition was held in central Georgia and Jenny and I went on Tuesday with huge thermals everywhere for their 63 mile triangular cross-country trip.

I was amazed at all the latest technology involved in something as simple as a hang-glider. The leading edges, up to the thickest point, have zillions of little squares, about 1/8th" square and .0010 thick, so I asked our guide about it. He said, "Just like the dimples on a golf ball, they provide extra lift." I told him that we always had super slick wings on our gliders and he replied that at 30-40 MPH, this works better.
,
Click to expand...

Ah..yes : Its related to my earlier post : Aerodynamicists refer to 'Reynolds number', which is a factor of speed / scale / viscosity (of fluid) etc.

Essentially, an airflow at a specific Re number (certain speed,scale, etc), will behave like a water-in-cornfield flow at the same Re (but therefore different speed, scale, etc... because viscosity of muddy water is different than air). This is why the aerodynamics that 'work' for an ASH25 sailplane at 120Kts (..polished, laminar-flow wing) do not work for a hang-glider : they're working at very different Re numbers.

..also incidentally, it's unlikely that the squares 'produce extra lift' (...other than very close to the stall) ..... more likely that they reduce drag (as they do on the golf ball), by turbulating the boundary-layer, which then stays attached to the wing, longer : it's not intuitive - a laminar boundary-layer reduces drag on the ASH25 (at 125kt!), but a turbulent boundary-layer may work better at hang-glider speeds.....
 
rv9av8tr said:
It's a great visual demonstration and how it can be that a small round wire can have the same drag as an entire airfoil.
Click to expand...

So to take this to a practical level, is there a Comm antenna available that is faired properly? Or are they all just round wire? Does the bent whip help much? Or is it a visual appeal kind of thing??
 
Tom I enjoyed your description and video

I keep a private record of all SARL races for every one of the 1,641 race flights to date and I thought it my be interesting to post the complete record of the race you refer to in your signature block. It is copied below. Did succeed in saving you corn crop from the water? Also from your signature block I see that you got your instrument rating and that you finished the RV-10 you were building. You do get things done! And still, you take time to play in the mud and share what you learn.

Bob Axsom

Rocket 100, 2010 11/20/10 Sport SX300 Smith, Mike 265.46 305.48
Rocket 100, 2010 11/20/10 Sport SX300 Musick, Stan 261.13 300.50
Rocket 100, 2010 11/20/10 Sport Lancair Legacy Sutter, Ernie 259.33 298.44
Rocket 100, 2010 11/20/10 HMU P-51D Mustang Hendrickson, Claude 256.44 295.10
Rocket 100, 2010 11/20/10 Sport FX EVO Rocket Martin, Tom 238.60 274.58
Rocket 100, 2010 11/20/10 FX Blue Glasair I TD Hammer, Bruce 229.78 264.43
Rocket 100, 2010 11/20/10 Sport Glasair III Gossen, Dick 227.99 262.37
Rocket 100, 2010 11/20/10 Sport FX F1 Rocket Nelson, Greg 225.85 259.90
Rocket 100, 2010 11/20/10 HM T-28 T-28B Johnson, Robert 225.75 259.79
Rocket 100, 2010 11/20/10 Sport FX F1 Rocket Hadath, Wayne 224.51 258.36
Rocket 100, 2010 11/20/10 Sport FX RV Super-6 Mills, Bob 216.41 249.04
Rocket 100, 2010 11/20/10 Sport FX EVO Rocket Frederick, Mark 215.79 248.33
Rocket 100, 2010 11/20/10 Sprint Glasair I RG Sherwood, Russell & Rhea 210.72 242.49
Rocket 100, 2010 11/20/10 RV Gold RV-8 Huft, John 205.39 236.36
Rocket 100, 2010 11/20/10 Sport FX EVO Rocket Fisher, George 202.94 233.54
Rocket 100, 2010 11/20/10 RV Gold RV-8 Ogden, Deene 196.89 226.58
Rocket 100, 2010 11/20/10 RV Blue RV-8 Rovey, Jason 195.44 224.90
Rocket 100, 2010 11/20/10 RV Gold RV-8 Hajek, Jerry 194.43 223.74
Rocket 100, 2010 11/20/10 RV Blue RV-7 Wilcox, Gary 193.72 222.92
Rocket 100, 2010 11/20/10 RV Blue RV-6A Axsom, Bob 192.80 221.87
Rocket 100, 2010 11/20/10 RV Gold RV-10 Nafsinger, Nick 191.47 220.34
Rocket 100, 2010 11/20/10 FAC1RG Bonanza S35 Jurskis, Chester 188.73 217.19
Rocket 100, 2010 11/20/10 RV Blue RV-8 Grover, David 187.39 215.65
Rocket 100, 2010 11/20/10 Sprint Long EZ Adams, David 182.98 210.57
Rocket 100, 2010 11/20/10 RV Blue RV-8 Hopkins, Dan 179.74 206.84
Rocket 100, 2010 11/20/10 RV Blue RV-6 Thompson, Mike 178.53 205.45
Rocket 100, 2010 11/20/10 RV Red RV-7 Baker, Seth 178.47 205.38
Rocket 100, 2010 11/20/10 RV Red RV-8 Jones, Bryan 177.27 204.00
Rocket 100, 2010 11/20/10 FAC1RG Bonanza S35 Bennett, Bobby 175.68 202.17
Rocket 100, 2010 11/20/10 FX Red Wittman Tailwind W-10 Hardage, Tim 173.20 199.32
Rocket 100, 2010 11/20/10 FX Red Mustang II Bordelon, Greg 165.86 190.87
Rocket 100, 2010 11/20/10 RV Blue RV-7A Hard, Jim 161.50 185.85
Rocket 100, 2010 11/20/10 FAC3RG Mooney (?) Kuhnel, Walter 143.75 165.42
Rocket 100, 2010 11/20/10 FAC3FX Cirrus SR20 Porter, James 142.89 164.43
Rocket 100, 2010 11/20/10 FAC3FX Cessna 182 Bennett, AnnElise 138.76 159.68
Rocket 100, 2010 11/20/10 FAC5FX Grumman AA5A Ely, Team 124.74 143.55
Rocket 100, 2010 11/20/10 FAC3FX Cessna 182 Sisk, Charlie 114.54 131.81
Rocket 100, 2010 11/20/10 FAC6 Cessna 150 Caponigro, Rich 98.98 113.91
 
Last edited:
Bob
Thanks for note, you and all other responders. Playing in the mud is something that all of us can relate to; who has not dragged there heel through a puddle of water and tried to get it to move somewhere else. I have watched this location a number of times over the years and it certainly gave me some real visual reasons for cleaning up the area around my cowling/gear leg intersections. One only has to look at a Lancair Legacy to see how clean an aircraft can be; and that the rewards of those design efforts show up time and again in race results.
 
BSwayze said:
So to take this to a practical level, is there a Comm antenna available that is faired properly? Or are they all just round wire? Does the bent whip help much? Or is it a visual appeal kind of thing??
Click to expand...

Relative to the oncoming wind, a bent antenna (round profile) will appear somewhat oval shaped. I haven't tried it, but have often thought that a bead of matching silicone RTV on the trailing edge, wiped to a V-shape would somewhat approximate a pressure recovery profile.

And if it doesn't work, you can peel it off.

It should be good for at least 5 knots. :rolleyes:

YMMV.
 
You must log in or register to reply here.